The invention relates generally to the paper handling features of a printer and more particularly to a switching mechanism for engaging and disengaging a paper holding roller for holding paper against the platen.
Printers are commonly used in connection with personal computers and word processors. Typically, the paper feeding mechanism of the printer includes a lever and bar for contacting paper holding rollers to recording paper to secure the paper to a platen during printing and releasing the rollers so that paper can be fed into the printer. As shown in FIG. 10, common paper holder switching mechanisms include a spring 205 to exert a large force on a bar 206 that supports a plurality of rollers 204 to hold the rollers firmly against a platen 203. Conventional printers commonly utilize the attractive force of a large solenoid 202 to rotate bar 206 to release rollers 204 from platen 203. When solenoid 202 pulls a bottom portion of bar 206 in the direction of arrow A, against the force of spring 205, paper holding rollers 204 separate from platen 203 in the direction of arrow S. When solenoid 202 is released, spring 205 holds paper holding rollers 204 against platen 203. Solenoid 202 must be powerful enough to overcome the substantial force of spring 205 which must exert sufficient force to properly secure paper to platen 203.
This conventional paper handling feature has shortcomings. If the printer is a manually operated printer, the paper rollers must be manually released from the platen each time paper is inserted or released. If the printer feeds paper automatically, a large solenoid is used to overcome the strong force of the spring that holds the rollers against the platen. Printers that utilize large solenoids to overcome the force of paper holding springs have durability and reliability problems and can be expensive.
Accordingly, it is desirable to provide an improved paper holder switching mechanism that does not require the a large solenoid and overcomes the shortcomings of the prior art.